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  • Nat. Hist. Res. , Vol. 7 No. 2: 193-197, March 2003

    Maternal Egg Care in the Bridled Triggerfish, sumαmen fr,αenαtus (Balistidae) at

    Hachijojima Island, Japan

    Hiroshi Kawase

    Coastal Branch of Natural History Museum and Institute, Chiba 123 Yoshio, Katsuura, Chiba 299-5242 , ]apan

    E-mail: h.kws@mc.pref.chiba.jp

    Abstract Maternal egg care in the trigger白sh Sufflamen fraenatus (Balistidae) based on underュ water observations are described for the first time. Females cared for the eggs on sandy bottoms and rocky reefs. The eggs were adhesive and attached to sand particles. They were nearly spherical in shape, measuring 0.54 mm in diameter. Egg masses measured an average length of 94 mmX74 mm , and one of which contained 91 ,500 eggs. The parental female positioned herself near the egg mass, often blowing water on it and driving away intruding 白sh. She blew water on the eggs vigorously in the evening of the spawning day to promote hatching, which behavior was similar to that found in the congeneric S. chηsoρterus. Not only parental egg care in S. fraenatus , but also that in S. chrysopterus, Melichthys vidua and Xanthichthys mento was record巴d at Hachijojima Island.

    Key words: parental care, spawning site, territoriality, demersal eggs, Tetraodontiformes.

    Triggerfish (family Balistidae), which inュ clude an estimated 40 species (Nelson, 1994), are widely distributed throughout the seas in tropical regions. The reproductive ecology such as spawning behavior, parental egg care and mating systems of several species have been reported based on underwater studies (e.g. Fricke, 1980; Gladstone, 1994; Kawase and Nakazono , 1994; Ishihara and Kuwaュ mura, 1996; Kuwamura, 1997). One characュ teristic behavior of this family is that the parental females care for eggs by blowing water on them and driving away intruders (Kawase, 1998, 2002). The bridled triggerfish Sufflamen fraenatus

    is found in the Indo-Western Pacific (Matsuュ ura, 1980), and is commonly seen in shallow waters in tropical and subtropical areas. Kawabe (1984) conducted aquarium observaュ tions and reported that S. fraenαtus spawn in the morning and that females care for the eggs until hatching in the evening. In this article, 1 describe the maternal egg care, spawning site, size of egg mass, clutch size and eggs of S. fraenαtus based on underュ water observations conducted at Hachijo・ jima Island, Japan. 1 also report on parental

    egg care in other balistids Melichthys vidua and S. chrysopterus observed at the same site.

    Materials and Methods

    Underwater observations of Sufflamenfrae司 nαtus were carried out on rocky reefs and sandy boUoms (10-20 m water depth) about 200m 0百shore of Sokodo (33008' N, 139048' E) , on the eastern coast of Hachijojima Island, Izu Islands, Japan. This study site is an oceュ anic island located in a temperate region, with annual water temperatures ranging from 15-290C. Observations of S. fraenatus were made in

    my spare time while 1 was studying another balistid species, Xanthichthys mento; these studies were carried out on 64 occasions beュ tween June and October from 1995 to 1998 (see Kawase, in press). When 1 found S. fraeュ natus females caring for eggs, 1 recorded the frequency of egg tending and guarding on a field map. Their behavior was also photoュ graphed and recorded on video. 1 then colュ lected a part of each clutch from 6 nests, collecting two or three times on the same day in three cases (Table 1). The diameters of the eggs and totallength of hatched larvae were

    -193一

  • Hiroshi Kawase

    Table 1. Spawning site, size of egg mass and embryonic development of Su.fflamen jraenatus.

    Code of Spawning Size of egg Embryonic Time of Water

    CMNH-ZF

    clutch Date

    site mass (mm) temparature

    No. development embryos fixed ---".(:-�

    A 11 Sep. 1995 cr early blastula 7:00 29.0 0004722

    Bl 17 Aug. 1996 cr 90X80 6・myomere 12:40 28.4 0004723

    B2 17-myomere 16:20 26.6 0004724

    B3 hatched larvae* 19: 25 26.5 0004725

    C 19 Aug. 1996 sb 115X 90 gastrula 10:20 26.5 0004726

    Dl 19 Aug. 1996 sb 105X90 gastrula 10:20 26.5 0004727

    D2 14-myom巴r巴 14:24 27.7 0004728

    E 19 Aug. 1996 cr 90X60 gastrula 10: 20 26.5 0004729

    F 29 Jun. 1997 cr 100X80 23.6

    G 24 Aug. 1997 cr 70X50 28.2

    Hl 25 Aug. 1997 cr 100 x 60 5-myomere 12: 30 26.9 0004730

    H2 hatched larvae* 18: 09 28.7 0004731

    cr, small cavity of rocky reef; sb, sandy bottom; ー, no data. *The eggs of clutches B and H collected at

    18: 28 and 17: 45 began to hatch, resp巴ctively.

    measured under a binocular microscope. The

    developmental stage of embryos was conュ

    firmed under an optic microscope in order to

    detect the time and date of spawning. In one

    case (Table 1 A) , 1 removed all the eggs from a nest in order to determine the size of the

    clutch. After fixing the eggs in 10% formaュ

    lin, sand particles attached to the eggs were removed and the total number of eggs was

    calculated following the method previously

    described (Kawase and N akazono, 1996; Kawase, in press). On those occasions on which 1 found other

    balistid species caring for eggs, 1 observed the behavior of the fish and collected a part

    of the clutch to examine embryonic developュ

    ment. The samples collected have been registered

    and are currently held by Coastal Branch of

    Natural History Museum and Institute, Chiba (CMNH-ZF・0004722-0004732~

    Results and Discussion

    1. Clutch and eggs of Sutnamen fraenatus

    A total of 8 clutches of S. fr,αenatus were

    found on the bottom (Table 1). Eggs were

    deposited in a small cavity of the rocky reefs

    (n ニ 6) (Fig. lA, B) or on the sandy bottom close to the reefs (n = 2) (Fig. 1 C, D). The mean length and width of the egg masses

    was 94 mm x 74 mm (n = 7), and clutch A conュ tained approximately 91 ,500 eggs. The size of the egg mass and the number of eggs in a

    194

    clutch were similar to those of the congeneric

    S.chηsoþterus (Kawase and Nakazono, 1994). The eggs were nearly spherical in shape,

    measuring 0.54士 0.01 mm (mean士SD, n= 15)

    in diameter. They were adhesive and at・

    tached to sand particles (Fig. 2), which is common among the other balistids (Kawase, 1998, 2002). The embryonic development of clutch D had atta;ned gastrula stage by 10:

    20 and 14-myomere stage at 14: 24. The

    clutch was not found the following morning.

    The eggs of clutches B and H had attained 5-

    6-myomere stage around noon. The eggs

    collected from the nests in the evening began

    to hatch, and the newly hatched larvae measュ ured 1.31 士 0.02 mm (mean:t SD, n = 10) and 1.25:t0.04 mm (mean:tSD, n=6) in total length, respectively. These results suggest that the spawning of S. fraenatus took place

    early in the morning and that the embryos

    hatched in the evening of the same day, which is consistent with aquarium observaュ

    tions (Kawabe, 1984). Such a short period from fertilization to hatching has also been

    reported in the other balistids, and seems to be characteristic of this family (Kawase, 1998, 2002).

    2. Maternal egg care in Sum.αmen frae-

    natus Parental females cared for the eggs deposュ

    ited on the bottom. During this time, males occasionally approached the females, howev-

  • Maternal Egg Care in lhe Triggerf�h

    Fig. 1. Maternal care and egg mass of Suffiamen JraenaLus. Egg-tending female with pale brown

    body color (A) and the 巴gg mass deposited in a small cavity of the reef (B) (clutch B, Table 1).

    Egg-tending female with blackish body color with a vertical white band on the caudal peduncle (C)

    and the egg mass deposited on the sandy bottom (D) (clutch D, Table 1). White arrows indicate the

    margin of the egg mass. 句

    Fig. 2. Photomicrograph of Suffiamen J,γaena­

    Lus eggs attached to sand particles

    er they soon departed without participating

    in parental care.

    The females care for the eggs by blowing

    water over them (2.22 bouts per min, obserュ

    vation time: 29 min 47 sec) (Fig. 1A, C) and removing remnants of algae from them (0.17

    bouts per min). The females also guarded the

    eggs, driving away intruding fish such as

    Gymnothorax sp. , Calotomus japonicus and

    Canthigαster valentini (0.20 bouts per min).

    Some females were aggr巴ssive and even atュ

    tacked the observer, while others were nervュ

    ous and retreated from the clutch site. The

    females did not devote time exclusively to

    egg care, but rather left the site in the dayュ

    time for 20-30 seconds at a time to feed

    within a few meters. Alternating egg care

    and feeding has also been reported in S

    chrysoρterus (Kawase and Nakazono, 1994;

    Ishihara and Kuwamura , 1996), although

    Pseudobalistes juscus females do not feed at

    all during egg care (Fricke, 1980). Kawabe (1984) reported that S. jraenatus

    females rapidly changed body color after

    spawning from pale brown with white

    blotches to uniformly blackish brown with a

    vertical white band on the caudal peduncle

    and maintained the darker color during egg

    care. The present study confirmed that body

    -